A fingerprint sensor is produced from an integrated circuit, in principle based on silicon, comprising especially an array of sensitive spots for generating a representation of the fingerprint of a finger placed directly on the surface of the array. Fingerprint detection may be optical or capacitive or thermal or piezoelectric.
Some sensors operate when a finger is placed statically on the surface of a sensor, the rectangular or square active detection array of which has an area corresponding to the fingerprint area to be detected; other sensors operate by the finger sliding over a sensor, the detection array of which, having a much smaller area than the fingerprint to be detected, is a thin elongate strip.
In both cases, but especially in the case of finger-sliding operation, the integrated circuit must be protected by wear-resistant layers. These layers depend on the type of sensor (for example, if it is an optical sensor, it is obvious that the optional protective layers must be protected by transparent layers). It has been proposed to use protective lacquers or else mineral coatings, such as silicon oxide coatings. Moreover, the integrated-circuit chip forming the core of the sensor must be electrically connected to the outside (especially to supply sources, control circuits and circuits for processing the electrical signals representative of the fingerprint). Given that the finger has to be placed on (or has to slide over) the sensitive surface of the sensor, this surface must remain accessible. This is why, for such sensors, a conventional electrical connection solution is adopted, using bonded flexible wires that connect contact pads on the front face (active face) of the integrated-circuit chip to contact pads located on a surface on which the chip is mounted. In integrated-circuit applications other than sensors (for example, microprocessors, memories, etc.), these wires are conventionally protected by a thick protective layer, deposited or overmolded, which encapsulates the chip and its wires.